An H bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. H bridge circuits are widely used in robotics and other applications to allow DC motors to run forwards and backwards. Most DC-to-AC converters (power converters), most AC/AC converters, the DC-to-DC push-pull converter, most motor controllers, and many other kinds of power electronics use H bridges. For example, a bipolar stepper motor is almost invariably driven by a motor controller containing two H bridges. An H bridge includes two pairs of switches with the load connected between the common switch/phase node of each switch pair. A common variation of the H bridge uses just one pair of switches on one side of the load, and is referred to as a half bridge. Half bridges are typically used in switched-mode power supplies that use synchronous rectifiers and in switching amplifiers. Another common variation adds a third ‘leg’ or even a fourth leg to the bridge configuration so as to realize a three-phase or four-phase converter.
Each leg of an H bridge, half bridge or multi-phase converter circuit includes a high-side switch and a low-side switch electrically connected at a common switch/phase node. The high-side and low-side switches are typically implemented as transistor dies such as power MOSFET (metal-oxide-semiconductor field-effect transistor) dies, which are often integrated in the same package such as a leadless or leaded molded package. Standard MOSFET dies have the source and gate terminals on the front side of the die and the drain terminal on the back side, which increases the resistance and inductance of the connection to the common switch/phase node of each transistor die pair.